CentOS 5.6 box locking up with memory error

I've just started getting this memory error and I'm not sure why. I'm utilizing quite a bit of squid processes and a "tunnel" process (proxy server), but this has never happened before. It's locking up the box and making it completely unusable.

I was able to view the console through xenserver. I have to force a reboot every time this happens.

I also have httpd/mysqld/vsftpd running but they are not doing very many requests. The problem started happening a few days after installing httpd/mysqld/vsftpd. Prior to this, the uptime on the box was over 6 months.

You are victim of the OOM Killer (out of memory error)
It looks like your httpd process is eating off memory. Monitor your server extensively and try to check what causes it. Has anything changed recently? That should be a start.

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mcaincAuthor Commented: 2012-04-05

The only thing that changed was that I added httpd/mysqld/vsftpd and then this started happening a couple of days later (when I began sending traffic).

Right now I'm looking at the overview of the server (via XenCenter) and there's only 9% CPU utilization and 969 of 6000mb of memory in use. This is with a reasonable traffic load.

The confusing part is that the machine was receiving relatively low amounts of traffic around both times that it crashed (once at 2am and once at 4am).

I also noticed that this machine does not have any swap configured. Could that help?